Maltotriose-producing amylases heretofore known are the enzymes derived from Microbacterium imperiale, Streptomyces griseus, Bacillus subtilis, Natronococcus sp., and Streptococcus bovis (Non-Patent Document 1). However, among these enzymes, only the Streptomyces griseus-derived enzyme is reported about its involvement with transglucosylation. In addition, this enzyme catalyzes transglucosylation only when the substrate concentration is high (the sum of the donor and acceptor substrates is 19%, 40% (w/v)), while catalyzes hydrolysis reaction alone when the substrate concentration is low (1% (w/v)), and will not catalyze transglucosylation (Non-Patent Documents 2 and 3). In addition, the enzyme is poorly resistant to heat, and thus is not used for food processing purposes.
Examples of industrially used glycosyltransferase include α-glucosidase used for the production of isomaltooligosaccharide or nigerooligosaccharide, β-fructofuranosidase used for the production of fructo-oligosaccharide or lactosucrose, β-galactosidase used for the production of galactooligosaccharide, α-glucosyltransferase used for the production of palatinose, cyclodextringlucanotransferase used for the production of cyclodextrin or coupling sugar, and branching enzymes used for the production of highly branched cyclic dextrin. Among these, α-glucosidase and branching enzymes act on polysaccharides and oligosaccharides containing α-1,4 bonds to catalyze transglucosylation. α-glucosidase catalyzes transglucosylation of monosaccharides, and branching enzymes catalyze transglucosylation of oligosaccharides containing four or more sugars or polysaccharides. There is no known enzyme which specifically catalyzes transglucosylation of maltotriose which is a trisaccharide.
In processed food containing starch, retrogradation of starch causes serious problems such as deterioration of storage stability. Retrogradation of starch is caused mainly by retrogradation of amylose molecules contained in starch, more specifically association of amylose molecules accompanied by insolubilization (Non-Patent Document 4). As a result of research on retrogradation control through starch depolymerization, retrogradation control is now possible to some degree. However, such depolymerized starch loses its intrinsic properties. In addition, decomposed starch has higher reducing power, and thus can react with a protein or amino acid when heated together, which results in coloring of the starch. Therefore, these methods have found limited applications (Patent Document 1). In order to solve these problems, studies for controlling retrogradation of starch without depolymerization have been carried out. For example, branching enzymes which decompose α-1,4 bonds of starch and synthesize α-1,6 bonds by transfer reaction are studied, but they have poor heat resistance, and thus are not used as food processing enzymes.